This program of research is aimed at investigating the role of the brain stem in the maintenance (and impairment) of sustained visual attention in trained monkey subjects. The function of brain stem neurons (specifically in the mesopontine reticular formation or MPRF) is studied by means of single-unit extracellular recording during the performance of various tasks. These tasks are designed to elucidate the role of MPRF neurons in supporting aspects of stimulus reception, stimulus processing and motor output that constitute, operationally, the process of attention. A guiding principle in this work is the possible relevance of this region of the brain for the pathophysiology of 'absence' attacks in petit mal epilepsy, and some studies are aimed more specifically at this question. These involve electrical stimulation of the MPRF intercurrently with performance, with dependent variables including behavior and characteristics of unit firing. Additionally, some behavioral and pharmacological studies involving anticonvulsant drugs are planned, to help test the adequacy of MPRF stimulation as a model of petit (absence) attacks.